This invention relates in general to a development station for a reproduction apparatus, and more particularly to a reproduction apparatus magnetic brush development station.
In typical commercial reproduction apparatus (electrographic copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics (hereinafter referred to as the dielectric support member). Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric support member. A receiver member, such as a sheet of paper, transparency or other medium, is then brought into contact with the dielectric support member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric support member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric support member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
One type of development station commonly utilized in electrographic reproduction apparatus is the magnetic brush development station. The magnetic brush development station includes a housing providing a reservoir for a supply of developer material. The developer material may be, for example, two-component material comprising magnetic carrier particles and relatively smaller pigmented marking particles. A mechanism, such as a paddle wheel, auger, or ribbon blender, is located in the reservoir and serves to stir the carrier particles and marking particles to triboelectrically charge the particles so that the marking particles adhere to the surface of the carrier particles. A transport mechanism brings the developer material into the field of a plurality of magnets within a rotating sleeve (commonly referred to as a toning roller). The rotating sleeve and magnetic field cause the marking particles to be brought into the vicinity of the latent image charge patterns on the dielectric support member to be applied to the latent image charge patterns in order to develop such patterns.
While magnetic brush development stations of the above described type are generally suitable for operation in present commercial reproduction apparatus, improvements in speed a range of use escalate the demands on all of the systems of the reproduction apparatus, especially the development station. For example, such magnetic brush development stations may create apparatus problems by the increased generation and control of marking particles dust. There can be several sources of marking particles dusting. Marking particle dust, if not sufficiently contained, can result in negative effects on image quality, reliability, and cost of ownership. That is to say, image quality is affected when other subsystems within the reproduction apparatus are contaminated with marking particle dust. For example, contamination of chargers results in non-uniform image densities due to non-uniform charging. Contamination of the exposure apparatus causes a non-uniform latent image and results in non-uniform image densities. Reliability can be effected when marking particles contaminates drive components, seals, and circuit boards. Increased customer and/or service personnel time to clean these components reduces the available up-time and productivity of the equipment.
In modern reproduction apparatus, reduction in the amount of marking particle dust generated has mostly been accomplished via materials changes to the carrier and/or marking particles. Mechanical changes that could be significant in reducing dust generation, i.e. core and shell speeds, also have the disadvantage of reducing development efficiency. Therefore, dust containment strategies have been actively pursued. Developer station dust containment strategies can consist of either active or passive controls. In most cases, a combination of these two techniques results in the best performance. Active controls generally are more complex, have impacts on other subsystems, need to be designed at the larger reproduction apparatus level, generate audible noise, and are more costly. These types of controls if not implemented correctly could influence air-flows within the system, cause additional reliability problems, or result in reduced marking particles yield. Passive controls are implemented at the subsystem level and have a reduced probability of influencing other subsystems. The simplest of passive fixes come in the form of seals or attempts at redirection of airflow in or around the development hardware.
One of the significant problems with the previously mentioned technologies is the generation of heat caused by the seal contacting the development roll surface. Other potential problems include, wear of the seal material, non-uniform contact of the seal material, contamination of the developer, etc. Generation of heat at or around the development roll surface has a high probability of generating marking particles flakes, which are unacceptable in high quality color digital imaging systems. Implementation of a magnetic seal that extends around at least a portion of the development roll, as described in U.S. Pat. No. 5,472,875, has the potential disadvantage of disrupting the material flow characteristics within the development housing.
In view of the above, this invention is directed to a magnetic brush development station for a reproduction apparatus. The magnetic brush development station includes:
a housing forming, at least in part, a reservoir for developer material, the reservoir having a pressure equalization seal;
a mechanism, associated with the housing for readily moving the housing relative to the reproduction apparatus;
a mechanism for selectively readily replenishing and/or emptying at least one component of developer material with respect to the reservoir,
a plurality of augers located in the housing for mixing developer material within the reservoir, a drive for the augers, the drive extending through the housing and having a seal therefore;
a development roller mounted within the housing for delivering developer material from the reservoir to a development zone, the development roller including a core magnet inside a shell, the core magnet and the shell having relative rotation, the core magnet extending less than the entire length of the development roller such that the developer nap on the shell does not extend to the end of the development roller;
a metering skive, extending the length of the development roller, for controlling the quantity of developer material delivered from the reservoir portion of the housing to the development zone, the metering skive positioned parallel to the longitudinal axis of the development roller at a location upstream in the direction of shell rotation prior to the development zone; and
a magnetic seal located in association with the skive at each end of the development roller, the magnetic field of the magnetic seal being sufficient to substantially prevent leakage of developer material from the ends of the development roller.
The invention disclosed here is a passive sealing technique that a) prevents airborne marking particles from escaping the developer sump and b) prevents marking particles from building up on the developer roll surface. The magnetic seal is made using a properly positioned magnet and developer already contained within the sump.
Preventing airborne marking particles from leaving the sump: The rotation of the development shell creates a flow of air that can pump airborne marking particles out of the developer sump. The development nap does not extend to the ends of the development roller. Hence a gap exists between the developer roller and the metering skive, allowing marking particles to escape via the air stream generated by the development roller. This magnetic seal is positioned near this gap to effectively seal marking particles in the sump.
Preventing marking particles from building up on the developer roll surface: In the pre-development zone region, fiber seals are used to contain marking particles dust. The developer nap/PC interface creates another seal. However, outside the developer nap, gaps between the development roll and PC allow airborne marking particles to migrate towards the ends of the development roller, can collect and build up on the development roll surface. If significant marking particles collects on the roller circumference, it can interfere with other surfaces, generate heat and produce flakes. The magnetic seal also serves to perform continuous wiping of the roller circumference.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.